Coating of paper and the like



Dec. 17, 1968 N. O. CLARK ET L COATING OF PAPER AND THE LIKE 2sheets-sheet 1' Filed April 29. 1965 FIGJ De c.17, l968 Filed April 29,1965 N. O. CLARK ET A.-

COATING OF PAPER AND THE LIKE 2 Sh e'e ts -Sheet 2 United States Patent3,416,943 COATING OF PAPER AND THE LIKE Norman Owen Clark and WilliamWindle. Cornwall. England, assignors to English Clays Lovering Pochin &Company Limited, Cornwall, England, a British company Filed Apr. 29,1965, Ser. No. 451.877 Claims priority, application Great Britain, May4, 1964, 18,510/64 Claims. (Cl. 117-44) ABSTRACT OF THE DISCLOSURE Anapparatus for coating sample sheet material comprises a backing roll fora sample sheet which is rotated to produce a peripheral speed equal tothe linear speed at which the sheet material will travel in a full scalecoating apparatus. A coating head with a reservoir for a coatingcomposition and a flexible blade for applying the coating composition toa sample sheet on the backing roll moves parallel to the axis ofrotation of the backing roll with the blade in contact with the sheetmaterial in such a manner that a sample sheet material mounted on thebacking roll is coated with a coating composition in the form of ahelical strip of coated sheet material having uncoated gaps left betweensuccessive turns of said helical strip.

This invention relates to apparatus for, and a method of, coating paperand like fibrous sheet materials.

It is known to apply coatings to paper and similar sheet materials for anumberof purposes, for example to increase the gloss, smoothness.opacity and brightness of the material, or to hide surfaceirregularities thereof, and in particular to improve the surface of thematerial so that it is capable of taking print in the best possiblemanner.

Such coatings generally consist of pigment bound with an adhesive. Thepigment which is used is principally kaolin or china clay, butalternatively others are used such as calcium carbonate, calciumsilicate. satin white, and titanium dioxide. The adhesive may be anatural protcin such as casein or soya, animal glue, starch, or asynthetic adhesive such as styrene butadiene, acrylonitrile or polyvinylacetate. These pigments and adhesives may be used as desired in a numberof combinations, and other additives may also be employed in thecoatings. The coatings may be applied in one or more layers.

The apparatus presently used for applying the coatings are of relativelyhigh capital cost. Furthermore they are costly to operate during theinitial starting-up period during which the working of the apparatus isinvestigated to ascertain the optimum conditions for operation using anyparticular machine, sheet material, and coating composition. In asimilar manner, the apparatus is expensive to operate for the purpose ofobtaining experimental data when designing new apparatus.

Hitherto, for experimental purposes, a small apparatus has been used,this apparatus being essentially a scaleddown version of productionapparatus. Such a scaleddown apparatus may have disadvantages,especiallywith regard to interpretation of results obtained therewith.In production apparatus, a blade is often used to spread the coatingcomposition, and such blade coating machines operate at high speed. Aweb of paper or the like sheet material may be run through the machineat a speed of between 1500 and 3000 feet per minute, and such highspeeds are difficult to attain in a scaled-down apparatus. Since theperformance of a blade coating machine is dependent partially upon thespeed at which the machine Patented Dec. 17, 1968 ICC is run, theresults obtained with a scaled-down apparatus may not be reliable. Onthe other hand, if full-size or scaled-down conventional apparatus isrun at a high speed, relatively large quantities of sheet material andcoating composition are necessary for a test, with the additional,consequential, problem that a large quantity of coated sheet materialneeds to be dried before laboratory testing. Laboratory testing is,however, generally carried out on small samples of material so that muchwastage may occur.

It is an object of the invention to provide apparatus and a method forthe experimental coating of paper and like sheet materials for testpurposes under conditions closely resembling those which prevail duringthe coating of sheet materials on a large scale.

According to one aspect of the present invention, there is provided forcoating sheet material, the apparatus comprising a rotatable backingroll upon which a sample of sheet material may be mounted to form acylinder. a coating head including a blade and a reservoir for receptionof coating composition. and means for enabling the coating head to bemoved in operation parallel to the axis of rotation of the backing rolland in contact with the sheet material mounted thereon whilst thebacking roll is rotated, whereby a helical strip of sheet material maybe coated.

According to an other aspect of the present invention, there is provideda method of coating sheet material, the method of comprising rotatingthe sheet material in the form of a cylinder about the axis of thecylinder and applying a coating to the sheet material by a coating headloaded with coating composition, the head being moved parallel to theaxis of the cylinder whilst the latter is rotated, thereby applying thecoating composition to a helical strip portion of the cylinder of sheetmaterial.

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made by way of example tothe accompanyin g drawings in which:

FIGURE 1 shows a general perspective view of apparatus for coating sheetmaterial,

FIGURE 2 is a perspective view of part of the apparatus, and

FIGURE 3 is a diagrammatic elevation illustrating the operation of theapparatus.

The apparatus shown in FIGURE 1 comprises a frame 1 upon which aremounted two aligned bearing blocks 2, only one of which may be seen inFIGURE 1. An axle 3 for a rubber-covered backing roll 4 is mounted forrotation in the bearing blocks 2. The backing roll 4 may be driven inthe direction indicated by arrow R by an electric motor 5 throughvariable speed gearing 6, pulleys and a belt 7. A carriageway comprisingtwo parallel bars 8 is mounted on the frame 1 so as to extend parallelto the horizontal axis of the axle 3 and at a level slightly below suchaxis.

Movably mounted by way of bobbin-shaped rollers 9 on the bars 8 is acoating head indicatedgenerally at 10. The coating head 10 is movablealong the carriageway with the aid of a hydraulic cylinder 11 and ram12, the cylinder 11 being mounted on the frame through the intermediaryof a bracket 11a. Power for the hydraulic cylinder and ram may besupplied from a hydraulic pump 13 mounted on the base of the frame 1 ofthe apparatus. Passage of hydraulic fluid from the pump 13 to thecylinder 11 is by way of pipes (such as the pipe ilb in FIGURE 2) inknown manner, and may be regulated by a control valve 14.

The construction and arrangement of the coating head 10 are more fullyillustrated in FIGURE 2. A platform is carried by the rollers 9 and hasmounted thereon two side pieces 16 between which is carried a bladesupport 17. A

curved blade 18 is clamped in known manner to the bot- 3 tom of theblade support 17. The blade is of spring steel of 0.2 to 0.4 mm.thickness, and comprises essentially a very short portion of aconventional coatingblade so that the vertical dimensions andconfiguration of the blade are conventional, whereas the width isgreatly reduced. The backing roll 4 is also of conventional dimensions,and may be 2 feet (60 cm.) in diameter and 3 feet (90 cm.) in length,whereas the blade 18 is only 3 or 4 inches in length, say 3 to 4 inches(about 8 to 10 cm.). A coating chamber 19 is formed by the blade 18 andtwo extentions 16a to the side pieces 16, such extension being curved toaccommodate the adjacent arc of the backing roll 4. The inner walls ofthe coating chamber are electroplated to resist chemical attack. Theextensions 160 forming the sides of the chamber 19 are fitted with feltedge seals 20. The blade 18 may be adjusted on a slider 21 by a togglearm 22 in a direction towards or away from the backing roll. Adjustingmeans (not shown) are also provided in known manner for varying theangle of the blade 18 with respect to the surface of the backing roll 4,for varying the pressure of the blade on the backing roll, and forvarying the vertical position of the blade with respect to the equatorof the backing roll. A tray (not shown) is disposed below the backingroll and the coating head for receiving excess coating composition inoperation.

For commencing operation, the coating head 10 is moved by conventionalmeans away from the backing roll 4, and is then brought to one end ofthe backing roll. it will be assumed for the purpose of this descriptionthat the coating head 10 is brought to the left-hand end of the roll asseen in the figures. A sample of the sheet material which is to becoated, and which may be of paper, for example, is wrapped around thebacking roll 4 and held in position by adhesive tape. The sample has awidth approximately equal to the length of the backing roll 4, and thelength of the sample is such that it may be wrapped completely aroundthe backing roll, with or without a little overlap. Thus the sample ofsheet material assumes the form of a circular cylinder. The backing roll4 carrying the sample is rotated in the direction indicated by the arrowR with the coating head 10 retracted away from the surface of thebacking roll until the latter has reached the desired speed of rotation.The peripheral speed of the backing roll and itssample may be equal tothe linear speed of the web of paper or-like sheet material in afull-scale coating apparatus. The coating head 10 is moved towards thesample of sheet material on the backing roll and is adjusted as desiredin respect of its position and its pressure on the sample.

When the various adjustments are complete, the appropriate coatingcomposition is poured into the reservoir 19 and the coating head 10 iscaused to traverse the backing roll 4 in the direction indicated by thearrow T by admitting hydraulic fiuid to the cylinder ll and therebyactuating the ram 12. At the end of the traverse of the coating head 10,the backing roll 4 is braked and the head 10 is removed from the surfaceof the sheet material on the stationary backing roll, thus dropping theunused coating composition into the tray (not shown) below the coatinghead 10. The speed of movement of the coating head 10 in the directionof the arrow T is controlled by the valve 14 in such a way as to producea spiral path of coated paper on the sample, which path if desired maycover substantially the whole surface area of the sample. Thus, for ahigher speed of rotation in the direction R, a higher speed of traversein the direction T is required.

FIGURE 3 shows diagrammatically the product of complete traverse of thecoating head 10. the coating head being shown in a position part wayalong the traverse.

The felt edge seals produce markings indicated at 23 in FIGURE 3. At theleft-hand end of FIGURE 3, there is shown in broken lines an edgemarking 230 which has been erased during the traverse. This marking 23ais one of the edge markings of an initial coated hoop 24 produced duringthe initial runningup period of the roll after the coating compositionhas been introduced into the reservoir 19 but before the traverse hasoccurred. After the traverse has been initiated, a helical path 25 isproduced extending the length of the cylinder. of sheet material on thebacking roll. A narrow gap 26 is left between each turn of the helix inthe product shown, but this gap may be removed if desired by suitableadjustment of the control 14. At the end of the helical path, thecoating head 10 is brought to a halt with the backing roll stillrotating so as to produce a coated finishing hoop 27, thereby erasingthe final part of the helical path. It will be seen that, apart from theends of cylinder, the sheet material is coated with only one coat ofcomposition and may be coated at a speed comparable with that ofproduction apparatus without producing a large quantity of coatedmaterial. The helical path 25 is disposed at an angle A of only about 2%to the direction of motion R of the sample of sheet material, so thatthe departure from truly linear coating is negligible. It is found inpractice that thereis no interference with the coating results, byvirtue of the sideways movement of the coating head 10, if the length ofthe blade 18 is about one-tenth of the length of the backing roll 4, as

- described above. However, if desired the blade 18 may be longer, beingup to about one-quarter or one-third of the length of the backing roll4, or may be even shorter than one-tenth of this length.

After the coating head 10 has been withdrawn from the sheet material,the latter is dried. This may be done either in situ, for example byradiant heat, or may be done by removing the sample from the backingroll and drying in a drying chamber, with for example hot air. Sinceonly a small quantity of coating composition is used on each sample,relatively little expenditure of heat energy is involved in the dryingprocess. After drying, the sample is cut into strips for examination.

It will be appreciated that a number of modifications may be made to theapparatus described above. For example, the carriageway may be replacedby a lathe carriage for the coating head 10. if desired, a mirror (notshown) may be disposed at a suitable angle above the coating head 10 sothat an operatormay be able to study the conditions prevailing withinthe reservoir 19. In this way the turbulence of the coating compositionmay be observed during operation.

We claim:

1. An apparatus, for coating sample sheet material, which comprises:

a rotatable backing roll upon which a sample of sheet material to becoated may be mounted to form a cylinder; 4 1 i first drive means forrotating said rotatable backing roll at a specific peripheral speedequal to a linear speed at which said sheet material will travel in afull scale coating apparatus;

a coating-head including a flexible blade having an edge which extendssubstantially parallel to the axis of rotation of said backing roll andhaving an operative length not more than one-third the operative lengthof said rotatable backing roll, and a reservoir for reception of acoating composition; and

a second drive means for moving said coating-head parallel to said axisof rotation of the backing roll with said blade in contact with thesheet material mounted thereon while the backing roll is rotated at saidspecific peripheral speed in a manner such that a-sample of sheetmaterial mounted upon the backing roll may be coated with a coatingcomposition to form a helical strip of coated sheet material havinguncoated gaps left between successive turns of said helical strip.

2. An apparatus, for coating sample sheet material,

which comprises:

a rotatable backing roll upon whicha sample of sheet 6 material to becoated may be mounted to form a 5. A method of coating sheet materialwhich comcylinder; prises the steps of: first drive means 'for rotatingsaid rotatable backing roll mounting said sheet material on a rotatablebacking at a specific peripheral speed equal to a linear speed roll toform a cylinder;

at which said sheet material will travel in a full scale 5 rotating saidbacking roll with the sheet material coating apparatus; mounted thereonat a specific peripheral speed equal a coating head mounted on rails andincluding a fiexto a linear speed at which said sheet material will ibleblade of spring steel, which is 0.2 to 0.4 millitravel in a full scalecoating machine;

meters thick and the edge of which extends substanapplying a coatingcomposition to said sheet material tially parallel to the axis ofrotation of said backing 10 from a coating-head loaded with a coatingcomporoll and has an operative length not more than onesition andincluding a flexible blade; having an edge third the length of saidrotatable backing roll, and which extends substantially parallel to theaxis of a reservoir for reception of coating composition; and rotationof said backing roll and having an operative length not more thanone-third the operative length of said rotatable backing roll, and areservoir for said coating composition; and moving said coating-headparallel to the axis of rotation of the backing roll, while the latteris rotated,

second drive means including a hydraulic rarn for enabling thecoating-head to be moved in operation along said rails parallel to theaxis of rotation of said backing roll with said blade in contact withthe sheet material mounted thereon while said backing roll is rotated atsaid s cific ri heral speed in a manner such that a s iple heet materialmounted of coawd having i gaps left upon said backing to" may bc coatcdwith a coating between successive turns of said helical strip.composition to form a helical strip of coated sheet References Citedmaterial having uncoated gaps left between succes- UNITED STATES PATENTSsive turns of said helical strip. I 3. Apparatus according to claim 2,wherein the operai'g gi g2 tive length of the edge of the flexible bladeof spring steel 2235'250 3/1941 ggg 'zg 7 09 is approximately one-tenththe length of the-backing roll. 3.162082 2/1965 Krikorian 118413 4. Anapparatus according to claim 2, wherein the coating-head is mounted onthe rails through the inter- ALFRED L. LEAVI'IT, Rrimary Examiner.mediary of a slide which may be moved in a direction R L BROWDY (m-am xsubstantially perpendicular to the axis of rotation of the backing roll,whereby said flexible blade may be moved towards or away from saidbacking roll. 117-152, 118-409, 413

at a speed such that there is formed a helical strip

